Light Emitting Diodes (LEDs) have many advantages over conventional light sources, such as incandescent, halogen and fluorescent lamps. These advantages include longer operating life, lower power consumption, and smaller size. Consequently, conventional light sources are increasingly being replaced with LEDs in traditional lighting applications. As an example, LEDs are currently being used in flashlights, camera flashes, traffic signal lights, automotive taillights and display devices.
One particular type of device that employs LEDs is a segmented display, such as a seven-segment display device. The current design available for Surface Mount Technology (SMT) segmented displays uses a Printed Circuit Board (PCB) as the substrate for LED attachment and electrical connections. The light source in these designs can either be an LED package or a bare LED chip in each segment of the display. The usage of pre-tested and binned LED packages in the assembly of segmented displays enables uniform display between segments in displays and also enables stacking of multiple displays.
One unfortunate drawback to current segmented display designs is that there is an air gap between the thin layer of diffused epoxy on the top portion of the display and the LED package itself. This air gap between the upper epoxy layer and LED package reduces diffusion, which, in turn, creates hotspots during light up. Hotspots in each segment produce uneven colors at the edges of the segment during light up. The physical phenomenon that causes the hotspots is due to the epoxy meniscus, which is a natural result of the air gap between the LED package and the epoxy.